1. Field of Endeavor
The present invention relates to a method for impregnating a high voltage insulation of a winding bar.
2. Brief Description of the Related Art
Winding bars have a conductive bar made of a plurality of interwoven strands, each having an insulating layer wrapped around its surface; the manufactured conductive bars have an insulation (main insulation) wrapped around their surface.
In order to manufacture the main insulation, typically a dry mica tape is wrapped around the conductive bar to define a plurality of layers that are then impregnated with a resin.
In this respect, U.S. Pat. No. 6,840,749 (“'749 patent”) discloses a device for impregnating the mica tape layers of high voltage winding bars.
According to the '749 patent and with reference to FIG. 1, the conductive bar 1, with the dry mica tape 2 wrapped around it, is first covered over its entire length by a flexible sleeve 3.
Then the flexible sleeve 3 (preferably contained in clamp shaped tools 4 that accommodate the sleeve 3 and the conductive bar 1 with the mica tape 2) is inserted into a pressure resistant tank 5.
A vacuum is then applied in the flexible sleeve 3, in order to extract the air contained in the mica tape 2 (mica tape may contain up to 50% air).
Then, pressure is applied in the chamber 7 between the pressure resistant tank 5 and the flexible sleeve 3 and impregnating resin is injected into the flexible sleeve 3 to impregnate the mica tape 3.
As the sleeve 3 is flexible, the differential pressure between the pressure of the chamber 7 and the pressure within the flexible sleeve 3 (being the pressure with which the impregnating resin is injected into the flexible sleeve 3) causes the flexible sleeve 3 to press against the mica tape 2.
Then the resin is cured.
In order to achieve a quick impregnation (the resin deteriorates after a prefixed time), the impregnating pressure (i.e., the pressure of the resin entering the flexible sleeve 3 to impregnate the mica tape 2) is quite high, for example 10 bar; therefore the pressure in the chamber 7 (i.e., inside of the tank 5) must be higher than 10 bar.
Even if this method proved to be quite efficient, it needs the large pressure resistant tank 5 (to withstand the high pressure to be applied therein; pressure resistant tanks are very costly components and, for these particular kind of impregnating plants, they could cost as much as 50% of the total cost of the impregnating plant.
U.S. Pat. No. 3,531,751 discloses a coil around which a mica tape is wrapped and, around the mica tape, a layer of armor tape is applied with a portion of the coil that is not covered by it.